The present invention relates to a full-wave rectifying circuit.
The use of a level sensor with a dynamic range as wide as 100 dB is generally known in a noise reduction system. FIG. 1 shows an example of a level sensor of this type. This level sensor has a logarithmic amplifier 10 for receiving an input signal through a resistor; amplifiers 12 and 14 for multiplying an output signal from the logarithmic amplifier 10, by +2 and -2, respectively; and diodes 16 and 18 whose anodes are connected to output terminals of the respective amplifiers 12 and 14 and whose cathodes are commonly connected. The output signals from the amplifiers 12 and 14 combined by the diodes 16 and 18 are supplied to a smoothing circuit 20 formed of a capacitor and a resistor, where they are smoothed to provide a DC output signal.
In this level sensor, an offset voltage is generated at the amplifiers 12 and 14 so that the DC components of the signals supplied to the diodes 16 and 18 may have different values. Disregarding the smoothing circuit 20, the combined output signals from the diodes 16 and 18 become offset every half cycle as shown in FIG. 2. When the offset in the combined output signals is great, the error in the output signal is great. Additionally, when the output signal is smoothed by the smoothing circuit 20, a large ripple component is superposed on the DC output signal. Furthermore, since the amplifiers 12 and 14 are of low gain type, it becomes difficult to compensate for the phase shift between the input and output voltages. It becomes thus necessary to use a capacitor of great capacitance to compensate for this phase shift, making the integrated circuit bulky and costly.